This invention relates generally to the field of magnetic data storage devices, and more particularly, but not by way of limitation, to incorporation of an integrated circuit system for self-writing servo and clock fields aligned in time and coherent in phase and frequency to servo and clock fields previously written on a disc drive.
Disc drives are used for data storage in modem electronic products ranging from digital cameras to computer systems and networks. Typically, disc drive includes a mechanical portion, or head disc assembly (HDA), and electronics in the form of a printed circuit board assembly (PCB), mounted to an outer surface of the HDA. The PCB controls HDA functions and provides an interface between the disc drive and its host.
Generally, a HDA comprises one or more magnetic discs affixed to a spindle motor assembly for rotation at a constant speed, an actuator assembly supporting an array of read/write heads that traverse generally concentric data tracks radially spaced across the disc surfaces and a voice coil motor (VCM) providing rotational motion to the actuator assembly. Modem disc drives typically utilize magneto resistive head technology that employs both an inductive element, for writing data to the data tracks and a magneto resistive element for reading data from the recording tracks.
Continued demand for disc drives with ever increasing levels of data storage capacity, faster data throughput and decreasing price per megabyte have led disc drive manufacturers to seek ways to increase the storage capacity and improve overall operating efficiencies of the disc drive. Present generation disc drives typically achieve aerial bit densities of several gigabits per square centimeter, Gbits/cm2. Increasing recording densities can be achieved by increasing the number of bits stored along each track or bits per inch (BPI), generally requiring improvements in the read/write channel electronics, and/or by increasing the number of tracks per unit width or tracks per inch (TPI), generally requiring improvements in servo control systems.
Servo fields written to the surface of the disc provide positional information used by the servo control system to control position of the read/write heads relative to the rotating magnetic disc. As TPI escalate, servo field writing techniques that incorporate servo track writers are unable to provide servo fields with sufficient accuracy to support the increased track densities.
One approach taken by disc drive manufacturers to improve servo control systems has been through the introduction of self-servo writing methods. One such method is described in U.S. Pat. No. 4,912,576, issued Mar. 27, 1990 to Janz. In Janz, one side of a disc is reserved for servo and the other side for data. Janz teaches a first servo track written at an outer edge on the servo side of the disc. Transducers are moved-in radially one half of a track, as indicated by the first phase servo track amplitude, and a first data-track is recorded on the data side of the disc. The transducers are again moved-in radially one half of a track, this time as indicated by the first data-track amplitude, and a second phase servo track is recorded on the servo side.
Another approach is described in U.S. Pat. No. 4,414,589, issued Nov. 8, 1983 to Oliver, et al. This reference teaches servo writing wherein optimum track spacing is determined by positioning one of the moving read/write heads at a first limit stop in the range of travel of the positioning means. Unfortunately, the Oliver reference does not disclose how to generate a clock track using the internal recording data heads, as an external clock head achieves this.
Yet another approach is described in U.S. Pat. No. 5,612,833 issued Mar. 18, 1997 to Yarmchuk, et al. This reference teaches a method of keeping self-propagated track errors from growing during a self-servo writing process through the use of timing circuitry for adjusting the relative timing of one or more sections of the servo pattern, a pattern generator for producing write data for propagation bursts and product servo patterns, a time delay unit for making fine adjustments in relative timing of one or more sections of the written pattern, amplitude detection circuitry for measuring the readback amplitude of written transitions, a memory for storing various quantities such as the measured values of the readback amplitudes and reference track values, a divider for normalizing instantaneous readback amplitudes by their corresponding original full-track amplitudes, a microprocessor sequence controller and a servo controller having variable control parameters to allow rapid stepping and settling followed by a special form of control during the write process that limits the growth of track shape errors while substantially rejecting mechanical disturbances. The Yarmchuk reference fails to disclose servo loop measurement circuitry implementation within the disc drive, but teaches the use of a commercially available personal computer together with a commercially available data acquisition plug-in board containing timing circuitry, an ADC, and a DAC.
In still another approach disclosed in U.S. Pat. No. 6,031,680 issued Feb. 29, 2000 to Chainer, et al., a product servo pattern burst is written to a first track, a second sequential product servo pattern burst is written to a second track while servoing on a third track. However, the Chainer reference fails to teach the circuitry used to implement the disclosed self-servo writing method.
Self-servo writing as a technology is faced with many challenges. One of these challenges is the ability to write information aligned in time and coherent in phase and frequency with information previously written to the disc. Delays between the write channel and read channel cause readback information to be frequency coherent but shifted in phase relative to the write signal, which is fed to the write channel. Additionally, circuit offsets in any synchronization system whether phase locked loop (PLL) based, or otherwise, present themselves as an additional phase (or time) offset relative to the desired written information. Therefore, challenges remain and a need persists for advancing integrated circuit systems incorporated within disc drives to advance the art of disc drive self-servo writing in an economical and effective manner that overcomes the constraints present in disc drive self-servo writing technologies.
The present invention provides a disc drive with a rotatable disc surface accessed by a positionable read/write head controlled by a positioning mechanism functioning under the control of a servo control loop that includes a write channel for generating write signals for writing data to the rotatable disc surface, a previously written reference mark written to the rotatable disc surface, a servo write clock generator phase lock loop circuit controlling timing for writing a reference mark in substantial time alignment and frequency and phase coherent with the previously written reference mark, a pulse detector circuit for creating logic level signals from the previously written reference marks, a pattern generator for generating reference mark write signals from the logic level signals detected by the pulse detector circuit for use in writing the reference marks to the rotatable disc surface, a multiplexer for switching between write signals from the write channel and reference mark write signals from the pattern generator for writing information and the reference mark respectively to the rotatable disc surface of the disc drive, a memory buffer for storing radial position correction tables and values for writing the reference mark to the rotatable disc surface, and a self-servo control and sequencing circuit synchronizing timing signals for writing the reference mark to the rotatable disc surface integrated into drive electronics.
In a preferred embodiment, a method self-writing additional servo field and clock field information respectively in substantial time alignment and phase and frequency coherent with a respective previously written servo field and clock field is used to form a data track on a rotatable disc surface of a disc drive, using a read/write head of the disc drive. The steps used to write the additional servo field and clock field information respectively in substantial time alignment and phase and frequency coherent with the respective previously written servo field and clock field include, measuring a difference in radial position, relative to a center of the rotatable disc surface, between a read element and a write element of the read/write head for use in writing the information field to the rotatable disc surface; selecting a data track of the rotatable disc surface for reading the previously written information field written to the selected data track and setting an initial phase correction value, corresponding to the selected data track, to zero in preparation for writing the information field to the selected data track; positioning the read element adjacent the selected data track while obtaining a phase lock of a servo write clock generator phase lock loop circuit using the previously written information field for use in writing the information field to the selected data track in substantial alignment in time and phase and frequency coherent with the previously written information field; and writing the information field to a second data track of the rotatable disc surface substantially aligned in time and coherent in phase and frequency with the previously written information field of the selected data track, while maintaining the phase lock of the servo write clock generator phase lock loop circuit to the previously written information field.
These and various other features and advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.